Battery charger with battery life judging function

Abstract

A charging device includes a battery voltage detecting circuit for detecting the voltage of a battery pack; and a microcomputer having RAM for temporarily storing a battery voltage detected by the battery voltage detecting circuit, and a CPU for calculating a battery voltage gradient from the battery voltage detected by the battery voltage detecting circuit and a battery voltage sampled a prescribed time earlier. The charging device determines that the life of the battery has expired when the voltage of the battery pack prior to charging is less than or equal to a prescribed value J and the battery voltage gradient within a prescribed time period after the start of charging is greater than or equal to a first prescribed value K. The charging device also includes a display circuit for notifying the user when the life of the battery pack has deteriorated.

1. A battery life judging device comprising:
 a battery voltage detecting unit that detects a first battery voltage before charging of a battery begins and second battery voltages at a first time and at a second time subsequent to the first time, wherein both said first time and said second time are subsequent to a time when charging of the battery begins; 
 a memory that stores the first battery voltage and the second battery voltage detected by the battery voltage detecting unit; 
 a battery voltage gradient calculating unit that calculates a battery voltage gradient from the second battery voltages detected by the battery voltage detecting circuit at said first and second times; and 
 a judging unit including first means for judging if the first battery voltage exceeds a predetermined voltage and second means for judging if the battery voltage gradient exceeds a first prescribed value, 
 wherein the judging unit judges that a life of a battery has expired when the first battery voltage does not exceed the predetermined voltage and the battery voltage gradient exceeds a first prescribed value. 
 
     
     
       2. The battery life judging device according to  claim 1 , further comprising a display unit that notifies a user of judgment results for the battery. 
     
     
       3. The battery life judging device according to  claim 2 , wherein the display unit emits a first light when the battery is judged to be healthy, a second light when the life of the battery is judged to be nearly expired, and a third light when the life of the battery is judged to be expired, wherein the first light, the second light and the third light are different in color. 
     
     
       4. The battery life judging device according to  claim 1 , wherein the judging unit further includes means for judging if the battery voltage gradient exceeds a second prescribed value which is less than the first prescribed value, and
 wherein the judging unit determines that the life of a battery has nearly expired when the battery voltage gradient within the prescribed time period after the start of charging is less than the first prescribed value and greater than or equal to a second prescribed value. 
 
     
     
       5. The battery life judging device according to  claim 1  wherein the judging unit further includes means for judging if the battery voltage gradient exceeds a second prescribed value which is less than the first prescribed value, and
 wherein the judging unit determines that the battery is healthy when the battery voltage gradient within the prescribed time period after the start of charging is less than the second prescribed value. 
 
     
     
       6. A battery life judging device comprising:
 a battery voltage detecting unit that detects a first battery voltage before charging of a battery begins and second battery voltages at a first time and at a second time subsequent to the first time, wherein both said first time and said second time are subsequent to a time when charging of a battery begins; 
 a memory that stores the first battery voltage and the second battery voltage detected by the battery voltage detecting unit; 
 a battery voltage gradient calculating unit that calculates a battery voltage gradient from the second battery voltages detected by the battery voltage detecting circuit at said first and second times; and 
 a microcomputer that implements a battery life judgment which includes first means for judging if the first battery voltage exceeds a predetermined voltage and second means for judging if the battery voltage gradient exceeds a first prescribed value, 
 wherein the judging unit judges that a life of a battery has expired when the first battery voltage does not exceed the predetermined voltage and the battery voltage gradient exceeds a first prescribed value, and 
 wherein a display unit indicates the judgment results while emitting lights of different color depending on the residual length of battery life.